In the cylinder inner peripheral surface finishing process, the roughness of the cylinder inner peripheral surface is measured, and in the past, if the arithmetic average roughness Ra exceeds the control value, the cutting tip was replaced. On the other hand, regarding the tip holder, in the past, it was replaced when a predetermined period from a start of use ends or when the number of the workpieces undergoing the process exceeds a predetermined number.
When checking and reviewing the drive pulleys of stroke endurance completion products which are produced in this controlling method, although most of them were the drive pulleys whose seal rings were not abraded, it was found that there were some drive pulleys whose seal rings were abraded. That is, since only the replacement of the cutting tip is managed or controlled using the arithmetic average roughness Ra as the control parameter, it is found that the roughness control of the cylinder inner peripheral surface is not sufficient to stably produce the drive pulley whose seal ring is not abraded (the drive pulley that does not make the seal ring abraded).
Thus, inventors of the present invention carried out a comparative experiment in which the surface roughness shape of the cylinder inner peripheral surface was measured with the drive pulleys categorized according to whether the abrasion appeared at the seal ring. This experiment result is shown in FIG. 9.
As is clear from the experiment result in FIG. 9, regarding the arithmetic average roughness Ra, a difference of a measurement value of the arithmetic average roughness Ra between an acceptable product that is the drive pulley whose seal ring is not abraded and a reject that is the drive pulley whose seal ring is abraded is small, i.e. the difference of the measurement value of Ra is a slight difference. This means that it is impossible to separate the drive pulleys into the acceptable product and the reject by the measurement value of the arithmetic average roughness Ra. Further, this proves that the management or control using only the arithmetic average roughness Ra described above has a possibility of including some drive pulleys whose seal ring is abraded.
Therefore, the inventors measured, at the same time, [Maximum height roughness Rz], [Skewness Rsk of roughness curve], [Kurtosis Rku of roughness curve] and [Reduced peak height Rpk (Protruding peak height Rpk)] which are the control parameters of the surface roughness shape except the arithmetic average roughness Ra. From this measurement result, it is found that regarding [Maximum height roughness Rz] and [Reduced peak height Rpk], their differences of the measurement value between, the acceptable product and the reject are small. In contrast, to this, it is found that regarding [Skewness Rsk of roughness curve] and [Kurtosis Rku of roughness curve], their differences of the measurement, value between the acceptable product and the reject are large. More specifically, in the case of the Skewness Rsk, there is a difference ΔRsk between the acceptable product and the reject, which indicates that the measurement value of the reject is three or four times as large as that of the acceptable product. In the case of the Kurtosis Rku, there is a difference ΔRku between the acceptable product and the reject, which indicates that the measurement value of the reject is more than twice the measurement value of the acceptable product.
Consequently, the inventors found from this comparative experiment that if at least one of [skewness Rsk of roughness curve] and [Kurtosis Rku of roughness curve] exceeds a predetermined value, the abrasion of the seal ring progresses.
Further, when the abrasion of the tip holder progresses due to long-term use and heavy-load use etc., stability or supporting performance of the cutting tip to the tip holder is impaired, and the cutting tip shakes or vibrates due to backlash caused by the abrasion, then this increases the measurement values of the Kurtosis Rku and the Skewness Rsk. That is, it is found that the progress of the abrasion of the tip holder is one of the cause of the increase in the measurement values of the Kurtosis Rku and the Skewness Rsk.
Here, the control value of the arithmetic average roughness Ra is a replacement judgment threshold value of the cutting tip 46. The control value of the arithmetic average roughness Ra is set, according to a correlation between Ra and Rku and a correlation between Ra and Rsk, to an Ra value that does not reach, a value that makes Rku and Rsk increased in each correlation.
The control value of the Kurtosis Rku is a replacement judgment threshold value of the tip holder 47. The control value of the Kurtosis Rku is set to a value that separates the drive pulleys into the acceptable product and the reject from a distribution of a plurality of measurement values of Rku.
The control value of the Skewness Rsk is a replacement judgment threshold value of the tip holder 47. The control value of she Skewness Rsk is set to a value that separates the drive pulleys into the acceptable product and the reject from a distribution of a plurality of measurement values of Rsk.
[Operation and Effect of Roughness Shape Control of Cylinder Inner Peripheral Surface]
As described above, it is found that the control or management of the roughness shape of the cylinder inner peripheral surface using the Kurtosis Rku and the Skewness Rsk as the control parameter is effective in suppressing the sliding abrasion of the seal ring. In the following description, operation end effect of the roughness shape control of the cylinder inner peripheral surface of the drive pulleys 12 and 22, to which this control using the Kurtosis Rku and the sieves so Rsk is applied, will be explained.
In the embodiment 1, each of the cylinder inner peripheral surfaces 12d and 22d of the drive pulleys 12 and 22 is set to the surface having the surface roughness shape whose measurement values of the Kurtosis Rku and the Skewness Rsk are the predetermined respective control values or less.
That is, in the case of “Rku>control value” or “Rsk>control value”, by the flow from step S4 or step S5 to step S7 in FIG. 5, it is judged that the replacement of the tip holder 47 is required. Then, on the basis of this judgment, the tip holder 47 is replaced. As a result, regarding the cylinder inner peripheral surfaces 12d and 22a of completed products of the drive pulleys 12 and 22, “Rku≤control value” and “Rsk≤control value” are achieved.
In this manner, the measurement values of the Kurtosis Rku and the Skewness Rsk which are closely related to the sliding abrasion of the seal rings 15 and 25 are used as the control parameter, and this is used for the control of the surface roughness shape of the cylinder inner peripheral surfaces 12d and 22d of the drive pulleys 12 and 22. Accordingly, it is possible to surely suppress the sliding abrasion, which decreases the sealing performance of the hydraulic chamber (the primary hydraulic chamber 14 and the secondary hydraulic chamber 24) provided at the drive pulleys 12 and 22, of the seal rings 15 and 25.
In the embodiment 1, each or the cylinder inner peripheral surfaces 12d and 22d of the drive pulleys 12 and 22 is set so the surface having the surface roughness shape whose measurement value of the arithmetic average roughness Ra is the predetermined control value or less and whose measurement values of the Kurtosis Rku and the Skewness Rsk are the predetermined respective control values or less.
That, is, in the case of “Ra>control value” and also “Rku>control value” or “Rsk>control value”, by the flow of step S3→step S4→step S7 or step S3→step S4→step S5→step S7 in FIG. 5, it is judged that the replacement of the tip holder 47 is required. Then, on the basis of this judgment, the tip holder 47 is replaced. As a result, regarding the cylinder inner peripheral surfaces 12d and 22d of completed products of the drive pulleys 12 and 22, “Ra≤control value”, “Rku≤control value” and “Rsk≤control value” are achieved.
Accordingly, since not only the Kurtosis Rku and the Skewness Rsk become the respective control values or less, but also the arithmetic average roughness Ra becomes the control value or less, it is possible to more surely suppress the sliding abrasion, of the seal rings 15 and 25.
In the embodiment 1, the liquid-tight seal member sliding on the cylinder inner peripheral surfaces 12d and 22d of the drive pulleys 12 and 22 is the seal rings 15 and 25 formed of the fluorocarbon resin as a material and shaped into the ring-shape.
That is, since the sliding abrasion of the seal rings 15 and 25 can be suppressed, the fluorocarbon resin having a good sliding abrasion, performance and a sealing performance can be applied to the liquid-tight seal member.
Thus, the sealing performance of the hydraulic chamber (the primary hydraulic chamber 14 and the secondary hydraulic chamber 24) provided at the drive pulleys 12 and 22 can be stably ensured.
Next, effect will be explained.
The drive pulleys 12 and 22 of the belt-drive continuously variable transmission CVT of the embodiment 1 obtain the following effects.
(1) A hydraulic actuator device (the drive pulley 12, 22) driven by being supplied with hydraulic pressure, has a piston-cylinder mechanism in which a liquid-tight seal member (the seal ring 15, 25) is set on an outer periphery of a piston (the fixed piston plate 16, 26) that is in sliding contact with an inner peripheral surface 12a, 22d of a cylinder 12b, 22b. 
As a control parameter of a surface roughness shape of the cylinder inner peripheral surface 12a, 22d, a kurtosis (Rku) of a roughness curve and a skewness (Rsk) of the roughness curve, each of which is a height direction characteristic average parameter, are used.
And the cylinder inner peripheral surface 12d, 22d is set to a surface having a surface roughness shape whose measurement values of the kurtosis (Rku) end the skewness (Rsk) are predetermined respective control values or less.
It is therefore possible so surely suppress the sliding abrasion, which decreases the sealing performance, of the liquid-tight seal member (the seal ring 15, 25).
Especially in the transmission of the vehicle, a filter is used in a hydraulic circuit to suppress a malfunction of a valve due to contaminants. Then if the seal member is abraded, filter clogging might occur due to powder particles caused by the abrasion, and this causes pressure loss in the hydraulic circuit. However, by suppressing the sliding abrasion of the seal member as described in the present embodiment, not only decrease of the sealing performance can be suppressed, but also an influence of the pressure loss on the entire hydraulic circuit can be decreased.
(2) An arithmetic average roughness (Ra) that is a height direction amplitude average parameter is added to the control parameter of the surface roughness shape of the cylinder inner peripheral surface 12d, 22d. 
And the cylinder inner peripheral surface 12d, 22d is set to a surface having a surface roughness shape whose measurement value of the arithmetic average roughness (Ra) is a predetermined control value or less and whose measurement values of the kurtosis (Rku) and the skewness (Rsk) are the predetermined respective control values or less.
Thus, in addition to the effect of (1), since the arithmetic average roughness (Ra) is added to the kurtosis (Rku) and the skewness (Rsk), it is possible to more surely suppress the sliding abrasion of the liquid-tight seal member (the seal ring 15, 25).
(3) The liquid-tight seal member sliding on the cylinder inner peripheral surface 12d, 22d is a ring-shaped seal ring 15, 25 formed of fluorocarbon resin material.
Therefore, in addition to the effects of (1) and (2), the sealing performance of the hydraulic chamber (the primary hydraulic chamber 14 and the secondary hydraulic chamber 24) provided at the drive pulleys 12 and 22 can be stably ensured.
(4) The cylinder is the cylinder 12b, 22b formed on a back side of the drive pulley 12, 22 of a belt-drive continuously variable transmission CVT, and the piston is the (the fixed piston plate 16, 26) fixed to the shaft portion of the drive pulley 12, 22 and forming she hydraulic chamber (the primary hydraulic chamber 14 and the secondary hydraulic chamber 24) in cooperation with the cylinder 12b, 22b. 
Therefore, it is possible to surely suppress the sliding abrasion, which decreases the sealing performance of the hydraulic chamber (the primary hydraulic chamber 14 and the secondary hydraulic chamber 24) provided at the drive pulleys 12 and 22 of the belt-drive continuously variable transmission CVT, of the liquid-tight seal member (the seal ring 15, 25).
Although the hydraulic actuator device of the present invention has been explained above on the basis of the embodiment 1, the specific configuration or structure is not limited to the embodiment 1 described above. Configuration or structure in the above embodiment includes all design modifications and equivalents belonging to the technical scope of the present invention.
In the above embodiment 1, as an example, the arithmetic average roughness Ra, the kurtosis Rku of the roughness curve and the skewness Rsk of the roughness curve are used as the control parameter of the surface roughness shape of the cylinder inner peripheral surfaces 12d and 22d of the drive pulleys 12 and 22. However, as long as at lease the kurtosis Rku and the skewness Rsk are used as the control parameter, for instance, instead of the arithmetic average roughness Ra, other control parameter could be used. Further, in the embodiment 1, the control values (the values by which the acceptable product and the reject are separated) of the kurtosis Rku of the roughness curve and the skewness Rsk of the roughness curve are used as the replacement judgment threshold value of the tip holder 47. However, the replacement judgment threshold value could be set to be smaller than the control value. In this case, because the tip holder 47 is replaced before Rku and Rsk of the produced drive pulley reach the control value, the drive pulley whose kurtosis Rku of the roughness curve, and skewness Rsk of the roughness curve exceed the respective control values can be prevented from being produced.
In the above embodiment 1, as the hydraulic actuator device, the drive pulleys 12 and 22 provided at the primary and secondary pulleys 1 and 2 of the belt-drive continuously variable transmission CVT are shown. However, the hydraulic actuator device of the present invention is not limited, to the drive pulley of the belt-drive continuously variable transmission. The hydraulic actuator device of the present invention can be applied to a variety of hydraulic actuator devices. That is, as long as a hydraulic actuator device is an actuator device that is formed, by a piston-cylinder mechanism in which a liquid-tight seal member is set on an outer periphery of a piston that is in sliding contact with an inner peripheral surface of a cylinder, and also is driven by being supplied with hydraulic pressure, the hydraulic actuator device of the present invention can be applied to this hydraulic actuator device.